This invention relates to a method of and an apparatus for determining the heights of points on an object on the basis of image signals from a camera unit.
Conventional methods of determining the heights of points on an object include a method illustrated in FIGS. 1 and 2.
In order to determine the heights (elevation) of various points in the regions of a photographed surface of an object, a pair of homologous points 13, 14 are determined on two images 11, 12, which will hereinafter be referred to as a "stereo pair", obtained by photographing the same region of a surface from two positions in different directions. The lines of sight 23, 24 for camera units 21, 22, by which the images 11, 12 have been obtained as shown in FIG. 2, are then determined on the basis of the location of these two points 13, 14 on the images 11, 12. The intersection of these lines of sight 23, 24 is then determined, and the three-dimensional coordinates of a point 26, which corresponds to the pair of homologous points 13, 14, on the surface 25 of the object is computed on the basis of a triangle formed by the camera units 21, 22 and the point 26. The above is the procedure for attaining the mentioned object. The methods, which can be used in such a procedure, of determining homologous points on a stereo pair include the known correlation method and SSDA (Sequential Similarity Detection Algorithm) method disclosed in, for example, "A Class of Algorithms for Fast Digital Image Registration" by Barnea and Silverman, IEEE, Trans, Compt. Vol. C-21, pp. 179-186, February 1972. Each of these methods consists of the steps of superposing a template including a point 13, of which the determination of a corresponding point is desired, on one image of a stereo pair on the other, and calculating the similarity thereof while sliding the template, to thereby determine the corresponding point 14 which has a maximum similarity. With such methods, a corresponding point cannot be determined correctly when the two images are distorted because the points lie on an irregular surface.